Four turtles fall into the sewers of New York City and are befriended by Hamato Yoshi, a Japanese man who lives in this subterranean refuge. One day Yoshi encounters a strange green glow of sewer sludge, which transforms him into a giant mutant rat named Splinter and the four turtles into humanoid creatures. Master Splinter dedicates his time to teaching the skills of the ninja to the turtles, who have become superpowerful from the radioactive waste floating in the sludge, and thus the Teenage Mutant Ninja Turtles (TMNT) are born.

In 1963 Marvel Comics was riding an unprecedented wave of sustained success with series such as The Fantastic Four,The Amazing Spider-Man, and The Uncanny X-Men, two of which featured superhero teams. But rival publisher DC Comics (coyly referred to by Marvel writer/editor Stan Lee as the Distinguished Competition) had already struck paydirt three years earlier with Justice League of America, which presented the company's best-selling heroes operating together as a crime-fighting team. Marvel's initial response to the Justice League of America (JLA) had been 1961's The Fantastic Four, which consisted of heroes created from whole cloth (with the exception of a second-generation Human Torch), because Marvel had no preexisting heroes then capable of competing with the likes of DC's Superman, Batman, Wonder Woman, the Flash, and Green Lantern. A mere two years later, the publishing landscape had changed considerably in Marvel's favor, enabling Lee and artist Jack Kirby to assemble enough successful Marvel headliners to form a supergroup title in the JLA mold with The Avengers (whose first issue bore a September 1963 cover date).

It can be argued that only those with very extreme personalities would don masks and tights to wage war on crime. Although neurotic superheroes like Spider-Man, intermittent multiple-personality sufferers such as the Hulk, or borderline psychopaths like the Punisher aren't unique in comics, superheroes whose costumed personae arise solely from a psychiatric disorder are rare indeed. The costumed martial-arts expert known as the Badger is one such hero.

The Black Cat is responsible for several firsts in her medium: She starred in the first comic from the legendary Harvey Comics, Pocket Comics #1 (in August 1941), and was the first and longest-lived Harvey superhero, in addition to being the first major costumed superheroine to grace comic-book pages.

Between 1979 and 1983, Spider-Man (Peter Parker) has to face life without Mary Jane Watson, the longtime love interest whom he is destined one day to marry. During this romantic interregnum, Parker's love life begins taking a decidedly unusual direction when he encounters Felicia Hardy, the talented burglar and platinum-blonde bombshell known as the Black Cat, who debuted in 1979 in The Amazing Spider-Man vol. 1 #194.

For much of the company's existence, DC Comics had been the comic industry's most conservative publisher, somewhat staid and reserved, but the rise of Marvel Comics and the success of the 1960s camp Batman television show changed all that. One of DC's responses to a growing superhero market that could stand a bit of comedy was to introduce the Inferior Five. It was one of the first self-referential strips, taking swipes at the whole superhero genre and its conventions, and—most satisfyingly—actually managed to be funny.

Musician Johnny Domino is having a good morning in San Francisco, until an alien energy bolt strikes a trolley car, sending a chunk of metal into his head. After he recovers, he learns that he does not need to sleep, his eyes are permanently dilated (making light painful), and that he can telepathically hear other people's evil thoughts inside his own head. Using his aikido training, Domino garbs himself in a costume and prowls the city rooftops after dark as the Night Man, to stop the crimes he knows are going to happen.

Comics scholars generally agree that Superman was the first true superhero of the comic books, clearing marking the entrance of a new kind of hero into the marketplace. Though Superman wears an iconic costume, he was not the first heroic character to do so. That honor goes to the Phantom, a mystery-man hero type who clearly ushered in the superhero genre. Written by Lee Falk (who earlier had success with the newspaper strip Mandrake the Magician) and drawn by Ray Moore, the Phantom first appeared in King Features Syndicate on February 17, 1936.